1. Technical Field
The present invention relates to a plate for lead storage batteries that is fabricated using a core material of expanded metal having a lozenge-shaped reticulated configuration produced from a slitted metal sheet by expansion thereof in a direction extending perpendicular to the slits, and packing the active material into cells of the expanded sheet, as well as to an apparatus for the manufacture of this plate.
2. Description of Related Art
Plates for lead storage batteries ordinarily consist of an active material packed into a mesh of a reticulated core material. As manufacture through casting offers few potential advantages in terms of improved productivity, such core materials are manufactured using expansion methods in which a lead or other metal sheet is expanded. These methods make continuous manufacture possible. Advantages of expansion methods are the ability to use materials of poor castability and the ability to manufacture thin plates. Expansion methods include the reciprocal process and the rotary process. The reciprocal process involves a serial procedure of intermittently feeding a metal sheet to a cutting die as the cutting die undergoes vertical reciprocating motion in a press in order to form slits, followed by expansion of the mesh. This method, however, is susceptible to changes in the dimensions of the metal sheet which can have an adverse effect on the final dimensions, and accordingly it is not possible to produce a fine mesh with uniform cells. Additional drawbacks are limited production speeds and the need for large-scale equipment. In contrast, in the rotary process the metal sheet is processed by feeding it between a pair of continuously rotated processing rollers provided with disk-shape cutters, thereby affording improvements in productivity.
The manufacture of core materials subjected to expansion by the rotary method using the production apparatus disclosed in Japanese Laid-Open Patent Application 55-61332, Japanese Laid-Open Patent Application 56-7357, and elsewhere is known. The production apparatus has a constitution like that depicted in FIG. 12. A metal sheet 2 in the form of a strip wound onto a coiler 1 is drawn out automatically from the coiler 1 and delivered to a reticulating machine 3. At the entrance to the reticulating machine 3 is provided a free-rotating roller 4 having two (left and right) flanged portions 7 disposed at a prescribed distance which corresponds to the width of the metal sheet 2. These serve to position the entering metal sheet 2 in the lateral direction. Thus, the metal sheet 2 is positioned in the lateral direction and is delivered, properly positioned, to the reticulating machine 3. The metal sheet 2 is passed through a pair of forming rolls 8 provided in the reticulating machine 3 and is thereby provided with peaks and valleys extending in a depthwise direction thereof (see FIG. 5), while at the same time creating a plurality of slits 9 extending in the forward direction.
Once the metal sheet 2 of strip form has been provided with peaks and valleys and with slits 9 by the reticulating machine 3, it is then continuously drawn out in the lateral direction by an expansion machine 10, thereby expanding the slit 9 portions into lozenge-shaped cells 11 to produce a lozenge-shaped reticulated configuration. The lozenge-shaped reticulated metal sheet 2 is then passed through a pair (upper and lower) of press rollers 13 provided to the press machine 12, thereby flattening out any warping, deformation, bending, or burrs produced during the reticulation and expansion processes, producing a continuous expanded metal sheet 14 of strip form. This expanded metal sheet 14 is cut to the prescribed dimensions and shape to produce core materials for lead storage battery plates.
As shown in the schematic perspective view given in FIG. 13, the expansion machine 10 comprises two side drive mechanisms 17 that open out from each other in the forward direction F from locations in proximity to the two lateral edges of the metal sheet 2 exiting the reticulating machine 3 and that convey the metal sheet 2 while pulling its two lateral edges outward, and a center drive mechanism 18 that conveys the metal sheet 2 while guiding the central portion (in the lateral direction) thereof in the forward direction F. Each of the conveyor mechanisms 17 and 18 is provided with a pair of chain members 19 (upper and lower); the metal sheet 2 is conveyed while retained from above and below between the pairs of chain members 19. The chain members 19 are driven around at constant speed in synchronized fashion by a connecting shaft 20.
Using designs such as those depicted in FIG. 14A and FIG. 14B, the side drive mechanisms 17 and the center drive mechanism 18 engage the metal sheet 2 in order to convey it. Specifically, as it passes through the reticulating machine 3, the metal sheet 2 is provided with engagement protrusions 21 disposed at both lateral edges and with an engagement protrusion 22 located in its central portion. The chain members 19 of the conveyor mechanisms 17 and 18 comprise, for example, of triplets of ordinary chains linked together.
In the side drive mechanisms 17, the engagement protrusions 21 are retained between two adjacent (left and right) chain links in the upper chain member 19, with the metal sheet 2 being held from above and below between the pair of chain members 19 so that the metal sheet 2 is gripped at its edges. The upper and lower chain members 19 are held by chain guides 23, with the top chain guide 23 being energized downward by a compression spring 24, forcing the two chain members 19 together so that pressure is applied to pinch the metal sheet 2. The upper and lower chain members 19, conveyed by means of chain guide holders 27 that hold the chain guides 23, advance so as to open out from each other in the forward direction F from locations in proximity to the two lateral edges of the metal sheet 2 as it exits the reticulating machine 3.
In the center drive mechanism 18, the engagement protrusion 22 is retained between two adjacent chain links located in the upper chain member 19, with the upper and lower chain members 19 retaining the metal sheet 2 through chain guides 28 which hold them. The center drive mechanism 18 prevents the central portion of the metal sheet 2 from moving in either direction as it is pulled outward by the two side drive mechanisms 17, conveying the sheet while guiding it in the forward direction F.
However, the production apparatus described above has several drawbacks. As is clearly evident from FIG. 13, the chain members 19 of the side drive mechanisms 17 and the center drive mechanism 18 are all driven at the same travel speed by the connecting shaft 20; however, the side drive mechanisms 17 travel diagonally outward with respect to the forward direction F, with the result that slippage occurs in a central area of the metal sheet 2 as it is conveyed by the center drive mechanism 18. Accordingly, the metal sheet 2 moves in such a way that its two lateral edges are conveyed faster than the central portion lying in the same plane. Referring to FIG. 15, L0&lt;L3=L4, as indicated by the alternate long and two short dashes lines, so expansion is not uniform between the central portion and the sides, resulting in wrinkles occurring in the central portion. Accordingly, the cells of the expanded sheet are not opened uniformly, resulting in a lozenge-shaped reticulated configuration in which the nodes connecting the cells are misplaced. Areas in which the openings in the metal sheet are larger than necessary are subjected to torsion and become extended, so that when the material is employed as a lead storage cell plate, the cell lattice rapidly experiences discontinuities due to corrosion, as well as falling out of the active material which has been packed into the cells. This results in shortened battery life.
Additionally, the side drive mechanisms 17 are designed to grip the sides of the metal sheet 2 and pull it outwards by means of the chain members 19; however, as gaps are present between the pins and links in the chain members 19, and gaps are also present between the chain guides 23 and the chain members 19, there are limits as to the accuracy of positioning with respect to the chain members 19. Wear is also a problem. Thus, the chain members 19 are not capable of accurately gripping the metal sheet 2 without chattering in order to convey it. This phenomenon also contributes to deviation in opening size when the metal sheet 2 is expanded, making it even more difficult to produce a high-quality core material. As noted in reference to FIG. 15, the chain members 19 of the side drive mechanisms 17 are pulled diagonally away from the forward direction F, and are thus subjected to a high bend load so that breakage of links due to fatigue is a frequent occurrence. It is therefor necessary to replace the chain members 19, which contributes to diminished productivity.